Experience indicates that ytrria-doped tetragonal zirconia polycrystal (Y-TZP) ceramic materials offer many advantages over conventional materials. Y-TZP is one of the toughest ceramics. The toughness is achieved at the expense of hardness and/or strength. A tetragonal zirconia alloy-alumina composite, that is, the product of sintering a particulate mixture of zirconia alloy and alumina, is another tough and relatively soft structural ceramic composite. Tetragonal zirconia polycrystal (TZP) ceramics and its composites are characterized by their high strength, high fracture toughness, superior wear, and abrasion resistances. Because of their attractive properties, these materials are suitable candidates for high precision punch, die, slitter knives, hydro-dynamic bearings, and machine components. Unfortunately, the manufacturing processes for these ceramics are difficult and are very costly primarily because of labor intensive machining processes to produce high precision complex shaped parts. Injection molding, however, is a technique which can be successfully utilized to manufacture large volumes of complex shaped parts in a cost effective way. Injection molding of inorganic powders with very fine particulate size, such as zirconia, and a wide variation in particle size such as in composites, pose a multitude of manufacturing problems, and the novelty of our invention relates to overcoming a plurality of manufacturing problems. In order to produce TZP, pure zirconia needs to be alloyed with a stabilizing agent(s), and the crystallite size needs to be maintained at a submicron level, preferably at or below 0.3 .mu.m. The composite ceramic materials of interest to this invention are composites of zirconia or alumina with either oxide or non-oxide inorganic particulates. Some of the examples of the composites in this invention are ZrO.sub.2 --Al.sub.2 O.sub.3, ZrO.sub.2 --TiB.sub.2, ZrO.sub.2 --SiC, ZrO.sub.2 --Si.sub.3 N.sub.4, ZrO.sub.2 --A1N, A1.sub.2 O.sub.3 --ZrO.sub.2, and other composites primarily based on inorganic oxides, carbides, nitrides, borides, and silicides. In the case of composites, the particle size distribution between the components of the composites normally have a wide range of variation.
Prior art searching in the field of injection molding of inorganic materials indicates that the inorganic materials normally have a narrow range of variation in their particle size distribution; injection pressure, temperature, and velocity are normally very high.
The prior art also fails to teach the use of ceramic composites having a wide variation of particle sizes in a low pressure, low temperature, and low velocity injection molding process.